Our goal is to determine if mature astrocytes present in intact brain exhibit functionally important membrane receptors for neuroactive substances. There is extensive evidence that astroglia isolated from immature brain and grown in culture express a variety of neurotransmitter receptor systems. However, there is little information concerning the functionality of these receptors on cultured cells and essentially no information regarding whether such receptor systems are expressed by mature astrocytes in brain. Recent studies indicate that receptor ligands that increase cyclic AMP levels in cultured astroglia stimulate the phosphorylation of glial fibrillary acidic protein (GFAP) in these cells. GFAP is an intermediate filament protein (IF-protein) unique to astrocytes. If neurochemicals influence the degree of phosphorylation of GFAP in intact brain, it should be possible to use this response to examine the influence of neurochemicals on astrocytes in intact brain. Furthermore, this system provides an approach for examining the influence of receptor ligands on intracellular events secondary to cyclic AMP metabolism in cultured astroglia. Thus, a number of questions concerning the pharmacological properties of astrocytes will be addressed. The following general questions will be addressed in this proposal. First, what are the mechanisms involved in the regulation of phosphorylation of GFAP in cultured astroglia? Second, are the same receptor systems involved in the regulation of phosphorylation of GFAP regardless of the brain region or brain age used to prepare cultures containing astroglia? Third, is phosphorylation of GFAP responsible for the shape change in astroglia that frequently occurs following receptor stimulation? Fourth, do receptor ligands affect the phosphorylation of GFAP in intact brain? Results from these experiments should enhance our knowledge concerning the manner through which neurons and astrocytes communicate during normal and abnormal brain function.